well, i could be wrong about this, but if high quality first scales, and then renders, you're still running on a pretty high resolution, no matter how small you're stage is, you are saving on texture space (if your objects are not scaled)
so i would say you should do both, for best performance
+ setting high dpi screens to no, actually if you don't scale you objects, this probably doesn't have an effect.
if you put a higher resolution objects and scale it smaller, on high dpi, it will show the details of the higher one.
but the best way to know is to do small tests, try some different settings,
but low quality scaling and no high dpi, should give you best performance, combine this with a smaller layout and you're set